Sepsis occurs when microbial invasion induces systemic illness (Bone (1996) Ann. Intern. Med. 125:680-687). Despite advances in modern hemodynamic, antibiotic, and ventilatory clinical support, sepsis represents a major clinical problem with no effective therapy (Angus, et al. (2001) Crit. Care Med. 29:1303-1310). There are 215,000 deaths related to sepsis in each year in the United States alone (Martin, et al. (2003) N. Engl. J. Med. 348:1546-1554; Hotchkiss & Karl (2003) N. Engl. J. Med. 348:138-15). Although the pathogenesis of sepsis-induced multiorgan injury leading to death is incompletely understood, it has been suggested that an initial hyperinflammatory process and subsequent immune paralysis contribute to mortality and morbidity in sepsis (Hotchkiss & Karl (2003) supra; Riedemann, et al. (2003) J. Clin. Invest. 112:460-467). The initial hyperinflammatory response seen in sepsis is associated with uncontrolled, exuberant cytokine production that can be deleterious to various tissues and can lead to organ injury and dysfunction (Benjamim, et al. (2004) J. Leukoc. Biol. 75:408-412; Oberholzer, et al. (2002) Crit. Care Med. 30:S58-S63). After this hyperinflammatory phase, an immune paralytic phase ensues with enhanced apoptotic cell death occurring in multiple organs including the spleen, kidney, liver, and heart (Ayala & Chaudry (1996) Shock 6:S27-S38).
Adenosine is a biologically active extracellular signaling molecule, which regulates a wide variety of immunological processes by binding to one or more of four G protein-coupled adenosine receptors (A1, A2A, A2B, and A3) (Németh, et al. (2006) J. Immunol. 176:5616-5626; Haskó, et al. (1996) J. Immunol. 157:4634-4640; Haskó, et al. (2000) FASEB J. 14:2065-2047; Németh, et al. (2003) Biochem. Biophys. Res. Commun. 312:883-888; Németh, et al. (2003) J. Pharmacol. Exp. Ther. 306:1042-1049; Németh, et al. (2005) J. Immunol. 175:8260-8270; Németh, et al. (2007) FASEB J. 21:2379-2388; Fredholm, et al. (2001) Pharmacol. Rev. 53:527-552; Jacobson & Gao (2006) Nat. Rev. Drug Discov. 5:247-264; Sitkovsky, et al. (2004) Annu. Rev. Immunol. 22:657-682). Adenosine is produced during inflammation, hypoxia, ischemia, or trauma (Haskó, et al. (1996) supra; Zhong, et al. (2005) Am. J. Respir. Cell Mol. Biol. 32:2-8; Chunn, et al. (2006) Am. J. Physiol. Lung Cell. Mol. Physiol. 290:L579-L587; Haskó, et al. (2002) Curr. Opin. Pharmacol. 2:440-444; Haskó & Cronstein (2004) Trends Immunol. 25:33-39; Blackburn, et al. (2000) J. Exp. Med. 192:159-170; Zhong, et al. (2004) Am. J. Respir. Cell Mol. Biol. 30:118-125), and because sepsis is associated with these metabolically stressful conditions, systemic adenosine levels reach high concentrations in mice and patients with sepsis and septic shock (Martin, et al. (2000) Crit. Care Med. 28:3198-3202). There is evidence to suggest that adenosine receptors can regulate the host's response to sepsis. For example, A1, A2B, and A3 receptors were found to decrease mortality, inflammation, renal dysfunction, and hepatic injury in murine cecal ligation and puncture (CLP), a clinically relevant model of polymicrobial sepsis (Gallos, et al. (2005) Am. J. Physiol. Renal Physiol. 289:F369-F376; Lee, et al. (2006) Am. J. Physiol. Regul. Integr. Comp. Physiol. 291:R959-R969; Csóka, et al. (2010) J. Immunol. 185:542-550). In contrast, it has been shown that A2A receptor activation contributes to the lethal effect of sepsis via decreased bacterial clearance, increased splenic apoptosis, and insufficient inflammatory cytokine levels (Németh, et al. (2006) supra). Thus, extracellular adenosine is an important regulator of immune events in mice undergoing sepsis and different adenosine receptors can have different and sometimes opposing effects on immunity during sepsis (Haskó& Cronstein (2004) supra; Haskó, et al. (2008) Nat. Rev. Drug Discov. 7:759-770; Haskó& Pacher (2008) J. Leukoc. Biol. 83:447-455).
One pathway leading to increased extracellular adenosine levels during metabolic stress is release of precursor adenine nucleotides, mostly ATP, from the cell followed by extracellular catabolism to adenosine by a cascade of ectonucleotidases, including CD39 (nucleoside triphosphate diphosphorylase) and CD73 (ecto-5′-nucleotidase) (Thompson, et al. (2004) J. Exp. Med. 200:1395-1405; Eltzschig, et al. (2004) Blood 104:3986-3992; Eltzschig, et al. (2003) J. Exp. Med. 198:783-796; Gessi, et al. (2008) Pharmacol. Ther. 117:123-140; Deaglio, et al. (2007) J. Exp. Med. 204:1257-1265). CD39 is a transmembrane molecule, which initiates extracellular adenosine generation by catalyzing the degradation of ATP and ADP to AMP (Haskó& Cronstein (2004) supra; Ernst, et al. (2010) J. Immunol. 185:1993-1998). CD73 is a 70-kDa glycosyl phosphatidylinositol-anchored cell surface protein with ecto-5′-nucleotidase enzyme activity that catalyzes the dephosphorylation of AMP to adenosine (Lennon, et al. (1998) J. Exp. Med. 188:1433-1443; Volmer, et al. (2006) J. Immunol. 176:4449-4458). Further, CD73 has been proposed to be the rate-limiting enzyme in the generation of adenosine during metabolic stress (Lennon, et al. (1998) supra; Eckle, et al. (2007) J. Immunol. 178:8127-8137). The immune regulatory functions of CD73 are well-documented in several in vivo experimental models. The anti-inflammatory action of methotrexate has been reported to be dependent on the adenosine-producing activity of CD73 (Montesinos, et al. (2007) Arthritis Rheum. 56:1440-1445). During LPS-induced acute lung injury, CD73-generated adenosine attenuates LPS-induced polymorphonuclear neutrophil (PMN) trafficking (Reutershan, et al. (2009) FASEB J. 23:473-482). Similarly, CD73-derived adenosine protects against bleomycin-induced lung injury (Eckle, et al. (2007) supra) and ventilator-induced acute lung injury (Eckle, et al. (2008) J. Clin. Invest. 118:3301-315). In hypoxia models, CD73 activity was required to prevent vascular leak and neutrophil infiltration into various tissues, indicating that extracellular adenosine produced during hypoxia is a potent anti-inflammatory signal for PMNs in vivo (Thompson, et al. (2004) supra; Synnestvedt, et al. (2002) J. Clin. Invest. 110:993-1002). A protective role of CD73-generated adenosine has also been shown in renal and myocardial ischemia (Grenz, et al. (2007) J. Am. Soc. Nephrol. 18:833-845; Eckle, et al. (2007) Circulation 115:1581-1590). Moreover, the use of alkaline phosphatase, CD39 and CD37 in the prophylaxis of a mammal at risk of inflammatory diseases has been suggested (WO 2008/104200 and WO 2009/106368).